COFDM Technology

 
Coded Orthogonal Frequency Division Multiplexing (COFDM) technology is the most advanced technology in signal processing for broadband communication over wireless. This technology is complex and offers significant improvements over standard modulation techniques such as the ones used in GSM systems, i.e., a strong robustness against echoes, and adaptability to mobile receivers. The main concept of COFDM is based on the fact that the effect of multi-path in broadband transmission is disastrous since echoes creates strong fading in the RF spectrum which can lose the entire signal if it is spread out over several MHz of bandwidth. COFDM splits the signal into several thousands of small spectrum (of a few kHz) which are independent from each other by using a Fourier Transform to generate the carriers, which has the particularity to orthogonalize each spectra with respect to each other.

The figure below shows the main difference between a standard single carrier communication scheme and COFDM.
 


As seen on this picture, the effect of channel multi-path (echoes) is dramatic with conventional single carrier systems, whereas it does not prevent to transmit data using COFDM. Therefore, COFDM is a very strong communication technique which is very well adapted to broadband bitrate in a wireless environment.

 Technology core
COFDM modulation is viewed by Dibcom as a core technology which will be used more and more in the years to come. The theoretical superiority of COFDM in wireless environment proves indeed that more and more digital standards will adopt COFDM as the physical layer modulation technique. Among these standards, some have already adopted COFDM (e.g. Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), Digital Audio Broadcasting in AM band) and some others are in the process to adopt it (e.g. IEEE 802.16.3, ETSI BRAN (Broadband Radio Access Networks), OFDM Forum).

In the field of Communications Integrated Circuits, especially in wireless transmissions, Dibcom believes that performance and power consumption are the key elements to succeed. Performance influences the coverage of transmission and therefore the number of satisfied customers who beneficiate from services. As the number of customers increases, the revenue for the operators increases which is the main driver for the business. The performance for Communication Integrated Circuits can be simply estimated as the Bit Error Rate versus the Carrier to Noise ratio or other degradation factors (e.g. Rayleigh fading, Saturation, Doppler effect, etc.). With a good core technology in COFDM, Dibcom is participating in the construction a great future of wireless broadband communications.

 Portability and Mobility
Portability and Mobility are new key elements for the coming years. As people travel more and need to communicate and have access to all information, whether they are at work, home, or anywhere else, it is necessary that most services such as voice, data, and leisure content become available anywhere on portable devices. However, portable devices imply important factors which need to be taken into account in the design of integrated circuits. Among these factors, the most important ones are reception performance and power consumption.
Reception performance in portable or mobile environment is a very different problem from fixed reception. Some additional problems and perturbations make the problematic much more complex.
These problems include:

  • Lower Carrier to Noise ratio
  • Dependence between the signal level and the receiver location
  • Varying echoes, Doppler effect
  • Interference created by multiple transmitters / receivers and movement
  • Sensitivity of the antenna